[aviralgarg05]

Fixes #172

Grid() now takes a native mrcfile object, not just a filename:

with mrcfile.open("density.mrc") as mrcobj:
    g = Grid(mrcobj)

The check is against mrcfile.mrcobject.MrcObject, so MrcFile and
MrcInterpreter both work, and so do subclasses like MrcMemmap and
GzipMrcFile.

Getting the data, header, origin and spacing out of an mrcfile object is
what reading a file already did, so I pulled that out of MRC.read()
into MRC._populate() and share it with a new classmethod
MRC.from_mrcfile(). That keeps the MRC-specific code in mrc.py and
leaves core.Grid with just the dispatch, along the lines of #162. Most
of the diff in mrc.py is that block moving one level out.

As discussed in the issue, the data are a view and are not copied. The
one caveat worth knowing is that a grid built from a memory-mapped
object loses its data when that object is closed; it is noted in the
docstring.

The interoperability docs still said loading from a native object was
not implemented, so I updated that section. It covers OpenVDB too, since
#170 landed that half already.

Tested with MrcFile, MrcMemmap, a gzipped file, MrcInterpreter,
and an object built in memory with no file behind it, plus the
non-volumetric, assume_volumetric and triclinic paths. A DX file
exported from a grid built this way is byte-identical to one exported
from the same file read from disk. Docs build clean.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.53%. Comparing base (313fde2) to head (bd44f45).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #186      +/-   ##
==========================================
+ Coverage   90.35%   90.53%   +0.18%     
==========================================
  Files           6        6              
  Lines         985     1004      +19     
  Branches      131      133       +2     
==========================================
+ Hits          890      909      +19     
  Misses         57       57              
  Partials       38       38              

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[read-the-docs-community]

Documentation build overview

📚 GridDataFormats | 🛠️ Build #35784811 | 📁 Comparing bd44f45 against latest (313fde2)

  🔍 Preview build  

7 files changed · ± 7 modified

± Modified

• genindex.html
• index.html
• gridData/core.html
• gridData/interoperability.html
• _modules/gridData/core.html
• _modules/gridData/mrc.html
• gridData/formats/mrc.html